In an aircraft cabin, an aircraft air-conditioning system usually ensures a necessary air exchange and controls the cabin pressure and cabin temperature. The term aircraft cabin is to be understood here as all areas of the aircraft which are to be ventilated during normal operation of an aircraft, such as, for example, a cockpit, a passenger cabin, crew areas, and cargo compartments which are to be ventilated. In large passenger aircraft with several engines, two redundant air-conditioning units which are independent of one another and run in parallel are generally provided in order to supply the aircraft cabin with breathable air. These air-conditioning units process engine bleed air and then feed it as process air into a mixing chamber. In the mixing chamber, the process air is mixed with recirculation air which is drawn from the aircraft cabin by suitable recirculation fans. The mixed air produced in the mixing chamber is finally distributed in the aircraft cabin via an air distribution system.
The cabin internal pressure is controlled by means of a cabin pressure control system which comprises controllable air outlet valves arranged in the fuselage of the aircraft. The air outlet valves of the cabin pressure control system are provided in the area of a skin of the aircraft fuselage. To control the cabin internal pressure, these air outlet valves are controlled in accordance with the pressure prevailing in the aircraft cabin and the flight status. A setting angle which these valves enclose with the skin is usually in a range between 0° and 90°. However, the air outlet valves are also drivable in such a way that their setting angle is greater than 90°. On the ground the air outlet valves are usually fully opened for cabin internal pressure reduction, i.e. their setting angle is 90°. During the flight phase, the setting angle of the air outlet valves in their normal operation is usually less than 90°.
If during the flight a fault in the aircraft air-conditioning system arises whereby the aircraft cabin can no longer be supplied with sufficient breathable air, the aircraft descends to a safe altitude and flies unpressurised to the destination airport or to an airfield situated nearer. In order to supply the necessary breathable air for the passengers during this period, it is known to provide aircraft with one or more so-called emergency ram-air inlets. In the event of failure of the aircraft air-conditioning system, an emergency ram-air inlet can be controlled such that ram air is fed from the aircraft environment directly into the air distribution system. In order to guarantee a sufficient breathable air supply, a suitable number of emergency ram-air inlets for the volume of the aircraft cabin are required.
An emergency ram-air inlet is an electrically driven, mechanical component and is therefore prone to faults. For reasons of redundancy, duplicate electrical drives of the emergency ram-air inlet must therefore be present. To control the emergency ram-air inlet, it is necessary to provide a control device which comprises sensors or limit switches in order to detect a limit of travel of the emergency ram-air inlet. Known emergency ram-air inlets are in general manually driven. Consequently, a suitable switch must be present in the cockpit. All additionally required devices and components increase the weight of the aircraft and thus reduce its payload capacity. In addition, each electrical drive of an emergency ram-air inlet has to be supplied with current. This permanently increases the required generator capacity, although the emergency ram-air inlets are driven only very rarely.